1. Field of the Invention
This invention relates to laser scanning systems and more particularly to a laser scanning system utilizing a bimorph optical beam deflector.
2. Description of the Prior Art
Bimorph optical beam deflectors for use in laser scanning systems and fiber optic scanning systems have been in existence for sometime. However, one major shortcoming is that the existing bimorph beam deflectors generally produce relatively small light beam deflections and they usually exhibit first mode oscillation, so that a mirror attached to the cantilevered end of the bimorph deflector travels through an arc and is physically displaced from one extreme end of the arc to the other. This physical displacement necessitates the need for further optical path controls to cause the reflected light beam to scan the appropriate area.
The article entitled "Bimorph Optical Beam Deflector" by J. F. Stephany et al, Applied Optics, Vol. 15, No. 2, February, 1976, Pages 307 and 308, disclose the typical bimorph light beam deflector with first mode oscillation. This article shows that some improvement in deflection angle is obtained by reducing the thickness of the piezoelectric layers of the bimorph crystal and by increasing the applied voltage thereto.
Russian Certificate of Invention No. 652,520 to Ashmarin et al, Mar. 18, 1979, discloses two cantilevered bimorph strips which are mutually perpendicular to each other with confronting loose ends engaging mutually perpendicular slots in opposing faces of a cubical member. Two adjacent perpendicular faces of the cubical member that are located between the slotted faces have photocells thereon which deflect light beams as the required angles. The bimorph strips oscillate in the first mode as disclosed in the above article by Stephany et al.
U.S. Pat. No. 3,614,677 to Wilfinger discloses a cantilevered semiconductor substrate capable of flexing in response to a change in temperature and is adapted to prompt flexing vibration predominantly at a resonant frequency in response to a heating means. An embodiment at FIG. 10 shows the substrate as a light deflection device which oscillates in the first mode.
U.S. Pat. No. 3,836,225 to Wilde et al discloses a fiber optic scanner. In FIG. 3, a bimorph transducer deflects horizontally about its longitudinal axis pivoting about its clamped end, when a sinusoidal voltage is applied. The fiber optic bundle is in the center of the bimorph transducer and along its longitudinal axis so that the first mode oscillation or repetitive horizontal deflection of the bimorph transducer sweeps the fiber optic bundle ends across the receiving fiber optics.
Japanese Patent Application No. 55-28757 to Kondou, published Oct. 2, 1981 without examination as Laid Open No. 56-125719, discloses a piezoelectric oscillator resting on supports near the ends thereof and having a mirror cantilevered from one of the end. The oscillator is oscillated in a manner so as to flex the oscillator centrally up and down over the supports. In this way, the flexing is produced with nodes at the supports. Although not operating in the first vibrating mode as in the above-mentioned prior art, this case does not mount the mirror at a node as is done in the present invention. Instead, Kondou discloses cantilevering the mirror at one end of the oscillator.
German Patent Application No. 30 35 314 A1 to Lauer, published without examination on Apr. 1, 1982 and assigned to Erwin Sick Gmbh Optik-Elektronik, discloses a resilient sheet attached at each end "A" and "C" which is oscillated by piezoelectric strips attached to the sheet between end A and a point B which is intermediate end C. Sheet end A is fixed and sheet end C is restrained by a strut. A mirror is attached at sheet end C. When the piezoelectric strips are excited by an A.C. voltage, the resilient sheet flexes about nodes B and C. However, the mirror at point C cannot remain on the horizontal axis of the resilient sheet for large deflections because this node is physically constrained by strut CD. The strut causes vertical motion of point C for large angular deflections of the mirror. In addition, this strut stiffens the system making it more difficult to drive.
U.S. Pat. No. 4,436,364 to Lauer et al discloses two coplanar cantilevered piezo-ceramic strips which have the free ends confronting each other and spaced apart a predetermined distance. A mirror is mounted via flexible legs to the free ends of the piezo-ceramic strips so that when an A.C. voltage is used to energize the strips in counterphase to one another, the mirror is moved with a rotary oscillation as the result of the counterphase movements of the free ends of the strips.
U.S. Pat. No. 4,385,798 to Yevick discloses the use of two cantilevered bimorph transducers, one of which has a free end that oscillates in one direction while the other end is attached to the other bimorph transducer's free end. This latter transducer free end oscillates in a direction perpendicular to the oscillation direction of the first transducer. A light pipe is centrally positioned through both bimorph transducers so as to directly project visible light on a viewing screen.
U.S. Pat. No. 3,981,566 to Frank et al discloses a hinged mounted linkage to couple a light beam deflecting mirror to the free end of a cantilevered bimorph transducer. The linkage employs flexible hinges to eliminate looseness between the mirror and the bimorph driver.